1. Field of the Invention
The present invention relates to a piezoelectric vibrator, a piezoelectric vibrator mounting body and a piezoelectric vibrator manufacturing method.
2. Description of the Related Art
In recent years, mobile telephones and portable information terminal devices employ a piezoelectric vibrator that uses crystal or the like as a time source, a timing source of control signals or the like, and a reference signal source etc. Various examples of this type of piezoelectric vibrator are known. One known example is a surface mount device type piezoelectric vibrator. As this type of piezoelectric vibrator, a three-layer structure type is generally known in which a piezoelectric substrate that has a piezoelectric vibrating reed formed thereon is bonded through being sandwiched by a base substrate and a lid substrate from above and below. In this case, the piezoelectric vibrating reed is housed in a cavity (a sealed chamber) that is formed between the base substrate and the lid substrate.
Further, in recent years, not only the above-described three-layer structure type piezoelectric vibrator, but also a two-layer structure type piezoelectric vibrator has been developed. This type of piezoelectric vibrator has a two-layer structure in which a base substrate and a lid substrate are directly bonded to each other, and a piezoelectric vibrating reed is housed in a cavity formed between the two substrates. The two-layer structure type piezoelectric vibrator is excellent in that it can be made thinner as compared with the piezoelectric vibrator having the three-layer structure, and is therefore preferably used.
As this type of piezoelectric vibrator, as disclosed in Patent Document 1 mentioned below, a structure is known in which a through hole is provided in a substrate (a base substrate) made of glass or ceramic, a wiring metal is formed on an inner surface of the through hole and upper and lower surfaces of a periphery of the through hole or on either one of the sections, an alloy is melted and welded to the through hole to cause the through hole to become an airtight terminal, and a crystal element (a piezoelectric vibrating reed) provided on a substrate surface is electrically connected to the alloy of the airtight terminal portion directly or via the wiring metal provided on the substrate surface. With this structure, it is considered possible to apply a predetermined driving voltage to the piezoelectric vibrating reed from outside the piezoelectric vibrator via the airtight terminal, namely, via a through electrode portion that is an electrode formed so as to penetrate through the substrate.
Generally, the piezoelectric vibrator has a structure with a positional relationship in which the through electrode portion is overlapped with the base substrate in a thickness direction while being sandwiched between the above-described wiring metals. This makes it easier to perform routing of a wiring electrode by connecting the wiring metal exposed to the outside of the piezoelectric vibrator (an external electrode portion) and the wiring metal exposed in the cavity (an internal electrode portion) through a shortest path.    Patent Document 1: JP-A-6-283951
However, with the piezoelectric vibrator and a piezoelectric vibrator manufacturing method disclosed in Patent Document 1, since the through electrode portion and the external electrode portion have the positional relationship in which the through electrode portion and the external electrode portion are overlapped with each other in the thickness direction of the base substrate, in a case in which the piezoelectric vibrator is mounted on a wiring substrate, bending stress applied to the piezoelectric vibrator is concentrated on the through electrode portion when the bending stress arises in the wiring substrate. At this time, the stress concentrated on the through electrode portion may cause a crack in a connecting part between the through hole and the through electrode portion. As a result, outside air circulates in the cavity, and this causes a problem in which a quality of the piezoelectric vibrator is affected.
The invention is made in light of the above-described problem, and it is an object thereof to provide a piezoelectric vibrator that has high mechanical strength when it is mounted on a wiring substrate.